Abstract

With the advent of precision guidance systems, maize (Zea mays L.) farmers in various tillage systems have more options in pre-plant nutrient banding relative to the intended crop rows. Anhydrous ammonia (NH3) placement during pre-plant application is of interest because of concerns for possible ammonia toxicity to maize seedlings when high NH3 rates are applied too close to the seed row and the need to improve plant-nitrogen (N) use efficiencies. Field studies were conducted between 2010 and 2012 near West Lafayette, IN, to compare traditional angled (diagonally) vs. precision-guided parallel NH3 applications (the latter was offset 15 cm from the future row) in no-till and conventional tillage systems. The NH3 was injected to depths of about 12 cm at N rates of 145 and 202 kg N ha–1. Maize was planted with additional starter N (20 kg N ha–1) within 6 d of NH3 application. Neither NH3 application placement resulted in significant maize seedling mortality. Conventional tillage increased mean grain yields across N rates and placement treatments from 10.6 to 11.6 Mg ha–1. Tillage did not impact reproductive-stage leaf chlorophyll content (SPAD), or whole-plant N content at maturity when NH3 was parallel applied, but these plant responses were significantly lower in no-till after diagonal application. Lowering the pre-plant N rate to 145 from 202 kg N ha–1 significantly lowered maize whole-plant biomass and N accumulation at maturity with diagonal application, but not when NH3 was parallel applied.

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